1. Field of the Invention
The present invention relates to a mobile communication system and an operation control method thereof, and more particularly, to a congestion control method of a radio access network system in a W-CDMA (Wideband-Code Division Multiple Access) communication system.
2. Description of the Prior Art
An architecture of a W-CDMA communication system including a mobile communication system is shown in FIG. 18. A radio access network (RAN) 1 is configured with radio network controllers (RNC) 4, 5 and Node B6 to 9, and is connected with a core network (CN) 3 as an switching network via an Iu interface. The Node B6 to 9 are logical nodes for radio transmission/reception, and more specifically, are radio base stations.
An interface between the Node B and RNC is referred to as an Iub, and an Iur interface is also standardized as an interface between RNCs. Each Node B covers one or more cells 10 and is connected to a mobile unit (UE) 2 via a radio interface. The Node B terminates a radio line, and the RNC manages the Node B and selectively combining and splitting radio paths. Note here that the detail of the architecture shown in FIG. 18 is specified in 3GPP (3rd Generation Partnership Projects).
FIG. 19 shows a protocol architecture of the radio interface in the W-CDMA communication system shown in FIG. 18. As shown in FIG. 19, the protocol architecture is composed of three protocol layers of a physical layer (PHY) 11 denoted as Layer 1, a data link layer 12 denoted as Layer 2, and a network layer (RRC: Radio Resource Control) 13 that is an upper layer of the data link layer 12 and is denoted as Layer 3. The data link layer of Layer 2 includes two sublayers of a MAC (Media Access Control) layer 121 and an RLC (Radio Link Control) layer 122.
An ellipse shown in FIG. 19 indicates a service access point (SAP) between layers or sublayers, where the SAP between the RLC sublayer 122 and the MAC sublayer 121 provides a logical channel. That is, the logical channel is provided from the MAC sublayer 121 to the RLC sublayer 122, and is classified by functions and logical characteristics of a transmission signal and characterized by contents of transferred information. The logical channel includes, for example, a common channel of CCCH (Common Control Channel), a paging channel of PCCH (Paging Control Channel), dedicated channels of DCCH (Dedicated Control Channel) and DTCH (Dedicated Traffic Channel), or the like.
The SAP between the MAC sublayer 121 and the physical layer 11 of Layer 1 provides a transport channel which is supplied from the physical layer 11 to the MAC sublayer 121. The transport channel is classified by a transmission form and is characterized depending on how and what information is transmitted via the radio interface. The transport channel includes, for example, a FACH (Forward Access Channel), a RACH (Random Access Channel), a PCH (Paging Channel), a DCH (Dedicated Channel), or the like.
The physical layer 11 and the data link layer 12 are controlled by the network layer (RRC) 13 via a C-SAP providing a control channel. The detail of the protocol architecture shown in FIG. 19 is specified in ARIB STD-T36-25.301v.3.8.
In the foregoing conventional art, there exists a C (Control) plane that controls signaling, and a U (User) plane that transports user data.
The RNCs 4, 5 of the radio access network (RAN) 1 in the conventional art are devices in each of which a processing function of controlling the C plane and a processing function of controlling the U plane are physically integrated. By using such a single device having the both processing functions integrated, a radio bearer service is provided to a terminal which is a mobile unit.
In the mobile communication system including such a conventional RNC that integrally has functions of U plane and C plane, if we need to enhance the function of the C plane, however the RNC itself should be added in the system. In the some way, if we need to enhance the function of the U plane, however the RNC itself should be added in the system. Therefore, the conventional RNC constitution makes constructing a system with high scalability quite difficult.
Moreover, there has been widespread data communication and image communication including moving pictures by using portable information terminals such as mobile telephones, notebook-sized personal computers, or the like, according to which user data transmitted through communication circuits increase in amount. This may consequently increase loads on a device handling the user data in the radio access network (RAN), causing a congestion state locally or system down in the worst case. Therefore, there now appeared the necessity of performing load distribution processing while continuing the processing for user data without causing system down even in the congestion state.